This invention relates generally to magnetic disk data storage systems, and more particularly to AMR read sensors for use in conjunction with magnetic data storage media.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk data storage systems 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (which will be described in greater detail with reference to FIG. 2). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to "fly" above the magnetic disk 16. Alternatively, some transducers, known as "contact heads," ride on the disk surface. Various magnetic "tracks" of information can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2 depicts a magnetic read/write head 24 including a write element 26 and a read element 28. The edges of the write element 26 and read element 28 also define an air bearing surface ABS, in a plane 29, which faces the surface of the magnetic disk 16 shown in FIGS. 1A and 1B.
The write element 26 is typically an inductive write element. A write gap 30 is formed between an intermediate layer 31, which functions as a first pole, and a second pole 32. Also included in write element 26, is a conductive coil 33 that is positioned within a dielectric medium 34. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16.
The read element 28 includes a first shield 36, the intermediate layer 31, which functions as a second shield, and a read sensor 40 that is located between the first shield 36 and the second shield 31, and suspended within a dielectric layer 37. The most common type of read sensor 40 used in the read/write head 24 is the magnetoresistive sensor. A magnetoresistive (MR) sensor is used to detect magnetic field signals by means of a changing resistance in the read sensor. When there is relative motion between the MR sensor and a magnetic medium (such as a disk surface), a magnetic field from the medium can cause a change in the direction of magnetization in the read sensor, thereby causing a corresponding change in resistance of the read element. The change in resistance can be detected to recover the recorded data on the magnetic medium.
One type of conventional MR sensor utilizes the anisotropic magnetoresistive (AMR) effect for such detection, including a soft adjacent layer (SAL) 42, a spacer layer 44, and MR stripe 46, and a cap layer 48, as shown in FIG. 3. The resistance of the MR stripe 46 varies in proportion to the square of the cosine of the angle between the magnetization in the MR stripe and the direction of a sense current flowing through the MR stripe. Because the magnetization of the MR stripe 46 can be affected when it is exposed to an external field, a detected change in resistance can be used to detect an external field.
More particularly, when the read sensor magnetization is properly biased, for example by transverse biasing, the change in resistance .DELTA.R is proportional to small external fields. Such transverse bias can be provided by a bias layer, or soft adjacent layer (SAL) 42, disposed near the MR stripe 46. Materials such as cobalt (Co) based alloys and nickel-iron (NiFe) alloys, for example nickel-iron-rhodium (NiFeRh), can be used as the SAL 42. However, to prevent exchange coupling and electrical shunting of the sensing current by the SAL 42, a nonmagnetic, electrically insulating film, or spacer layer 44, is interposed between the SAL 42 and the MR stripe 46. The spacer layer 44 should, accordingly, have high resistivity, as well as substantially zero magnetic moment (i.e., be non-magnetic). Also, the better the thermal stability of the spacer layer 44, the larger the maximum sensing current can be. In addition, a cap layer 48 can be included to protect the MR stripe 46 from oxidation that might degrade the sensor performance.
A performance parameter of such an MR sensor is the ratio of change in resistance, .DELTA.R, to the read sensor sheet resistance, R. This ratio, .DELTA.R/R, is sometimes referred to as the MR coefficient of the read sensor, with higher values indicating higher performance. Higher .DELTA.R/R can be achieved with thicker layers, however higher data density applications require thinner layers. As an alternative, .DELTA.R/R can be increased by heating the MR stripe 46 during fabrication, however, .DELTA.R/R is not increased if reactive layers are interfacially adjacent the MR stripe 46. Further, such heating can damage other layers, such as the shields 31 and 36. Therefore, instead of heating, .DELTA.R/R can be increased by forming the MR stripe on certain materials that are used as a seed layer.
Such a material that yields higher .DELTA.R/R when the MR stripe is formed on it, is tantalum (Ta). Also, because of its high resistivity, good thermal stability, and non-magnetic properties, tantalum (Ta) has been used for the spacer layer 44, as shown in the read sensor 40 of FIG. 3.
It has been proposed to use NiFeCr as a seed layer and spacer 52 between an MR stripe 46 and a SAL 42 in place of tantalum, as shown in the read sensor 50 of FIG. 4 to achieve greater performance. However, it has been found that when a material such as NiFeRh is used for the SAL 42, such a structure exhibits an undesirably low .DELTA.R/R. In particular, a NiFeRh/NiFeCr/MR read sensor exhibits a .DELTA.R/R on the order of less than 1.3%.
Thus, what is desired is an improved read sensor that results in a higher .DELTA.R/R, and therefore higher read performance, while minimizing sensing current shunting, and maximizing the allowable sensing current level.